Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932543AbdGKJEF (ORCPT ); Tue, 11 Jul 2017 05:04:05 -0400 Received: from mail-wr0-f194.google.com ([209.85.128.194]:33768 "EHLO mail-wr0-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932266AbdGKJEC (ORCPT ); Tue, 11 Jul 2017 05:04:02 -0400 Date: Tue, 11 Jul 2017 11:03:58 +0200 From: Ingo Molnar To: Kyle Huey Cc: Mark Rutland , gregkh@linuxfoundation.org, Peter Zijlstra , Vince Weaver , "Jin, Yao" , stable@vger.kernel.org, Alexander Shishkin , Arnaldo Carvalho de Melo , Jiri Olsa , Linus Torvalds , Namhyung Kim , Stephane Eranian , Thomas Gleixner , acme@kernel.org, jolsa@kernel.org, kan.liang@intel.com, Will Deacon , open list , "Robert O'Callahan" Subject: Re: [PATCH] perf/core: generate overflow signal when samples are dropped (WAS: Re: [REGRESSION] perf/core: PMU interrupts dropped if we entered the kernel in the "skid" region) Message-ID: <20170711090358.6si4un4guz6dbxkz@gmail.com> References: <20170628101248.GB5981@leverpostej> <20170628105600.GC5981@leverpostej> <20170628174900.GG8252@leverpostej> <20170704090313.xyb5lntyy55ga7dm@hirez.programming.kicks-ass.net> <20170704093345.GB19649@leverpostej> <20170704102159.GB20062@leverpostej> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: NeoMutt/20170113 (1.7.2) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1880 Lines: 41 * Kyle Huey wrote: > On Wed, Jul 5, 2017 at 10:07 PM, Robert O'Callahan wrote: > > On Tue, Jul 4, 2017 at 3:21 AM, Mark Rutland wrote: > >> Should any of those be moved into the "should be dropped" pile? > > > > Why not be conservative and clear every sample you're not sure about? > > > > We'd appreciate a fix sooner rather than later here, since rr is > > currently broken on every stable Linux kernel and our attempts to > > implement a workaround have failed. > > > > (We have separate "interrupt" and "measure" counters, and I thought we > > might work around this regression by programming the "interrupt" > > counter to count kernel events as well as user events (interrupting > > early is OK), but that caused our (completely separate) "measure" > > counter to report off-by-one results (!), which seems to be a > > different bug present on a range of older kernels.) > > This seems to have stalled out here unfortunately. > > Can we get a consensus (from ingo or peterz?) on Mark's question? Or, > alternatively, can we move the patch at the top of this thread forward > on the stable branches until we do reach an answer to that question? > > We've abandoned hope of working around this problem in rr and are > currently broken for all of our users with an up-to-date kernel, so > the situation for us is rather dire at the moment I'm afraid. Sorry about that - I've queued up a revert for the original commit and will send the fix to Linus later today. I've added a -stable tag as well so it can be forwarded to Greg the moment it hits upstream. We should do the original fix as well, but in a version that does not skip the sample but zeroes out the RIP and registers (or sets them all to -1LL) - and also covers other possible places where skid-RIP is exposed, such as LBR. Thanks, Ingo